Method for manufacturing MEMS microphone

ABSTRACT

The invention provides a method for manufacturing a MEMS microphone. The method comprises steps of: preparing a base; forming a first diaphragm on a first surface of the base; preparing a back plate; forming a first gap between the first diaphragm and the back plate; preparing a second diaphragm opposite to the first diaphragm; forming a second gap between the second diaphragm and the back plate; preparing electrodes on the second diaphragm; forming a back cavity by etching a second surface of the base opposite to the first surface.

FIELD OF THE PRESENT DISCLOSURE

The invention relates to the technical field of transducers forconverting soundwaves into electrical signals, in particular to amicrophone and a method for manufacturing a microphone by MEMS process(Micro-Electro-Mechanic Systems).

DESCRIPTION OF RELATED ART

With the development of wireless communication, the users haveincreasingly higher requirements for the call quality of mobile phones,and the design of microphone as a speech pickup device has a directinfluence on the call quality of mobile phone.

As MEMS technology is featured by miniaturization, good integratability,high performance, low cost and the like, it has been appreciated by theindustry, and MEMS microphone is widely used in current mobile phones;the common MEMS microphone is capacitive, i.e., including a vibratingdiaphragm and a back plate which both constitutes a MEMS Acousticsensing capacitance, and the MEMS acoustic sensing capacitance furtheroutputs an acoustic signal to a processing chip for signal processing byconnecting to the processing chip through a connecting plate. To furtherimprove the performance of MEMS microphone, a dual-diaphragm MEMSmicrophone structure has been proposed in the prior art, i.e., twolayers of vibrating diaphragm are used to constitute a capacitancestructure with the back plate respectively. In the MEMS microphone basedon silicon technology, the vibrating diaphragm and back plate of theabove MEMS microphone are on the same silicon foundation and made withsemiconductor making process, and it also comprises process steps suchas forming an acoustic cavity, back cavity, acoustic hole, venting holeand connecting plate during manufacturing.

As each making process step of MEMS microphone is to make and form onthe same silicon base, each process step can only be conducted after theprevious process step is finished, thus causing a relatively lowefficiency of manufacturing MEMS microphone.

Based on the above problems, it's necessary to provide a new method formanufacturing MEMS microphone dual-diaphragm structure to improvemanufacturing efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the exemplary embodiment can be better understood withreference to the following drawings. The components in the drawing arenot necessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the present disclosure.

FIG. 1 is an illustration of a MEMS microphone in accordance with afirst embodiment of the present invention.

FIG. 2 is an illustration of a MEMS microphone in accordance with asecond embodiment of the present invention.

FIG. 3 is a flow chart of a method for manufacturing the MEMSmicrophone.

FIGS. 4A-4V indicate the steps of the method for manufacturing the MEMSmicrophone.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present disclosure will hereinafter be described in detail withreference to several exemplary embodiments. To make the technicalproblems to be solved, technical solutions and beneficial effects of thepresent disclosure more apparent, the present disclosure is described infurther detail together with the figure and the embodiments. It shouldbe understood the specific embodiments described hereby are only toexplain the disclosure, not intended to limit the disclosure.

With reference to FIGS. 1-2, a MEMS microphone structure 100 prepared bythe manufacturing method of the invention comprises a base 101 and acapacitance system 103 placed on the base 101 and insulatively connectedwith the base 101.

The material of the base 101 is preferably semiconductor material, suchas silicon, which has a back cavity 102, a first surface 101A and asecond surface 101B opposite to the first surface, an insulation layer107 provided on the first surface 101A of the base 101 with a backcavity 102 through the insulation layer 107, and the first and secondsurfaces of the base 101. Wherein the back cavity 102 can be formedthrough corrosion by a bulk-silicon process and dry method.

The electric capacitance system 103 includes a back plate 105 and afirst diaphragm 104 and a second diaphragm 106 which are opposite to theback plate 105 and are respectively arranged on both sides of the backplate 105. An insulation layer 107 is arranged between the firstdiaphragm 104 and the back plate 105, between the second diaphragm 106and the back plate 105, and between the first diaphragm 104 and the base101. The central main body area of the back plate 105 includes anacoustic through-hole 108 arranged at intervals. In the presentinvention, the central main body area of the back plate 105 is, forexample, the area corresponding to the back cavity 102, and the areaoutside this area is the edge area of the back plate 105. The supportingcomponent 109 fixedly connects the first diaphragm 104 and the seconddiaphragm 106 through the acoustic through hole. Specifically, thesupporting part 109 is abutted with a top surface of the first vibratingdiaphragm 104 and a bottom surface of the second vibrating diaphragm 106respectively. The insulation layer 107 separates the first diaphragm 104and the back plate 105 for a certain distance and forms a first gap 110,and separates the second diaphragm 106 and the back plate 105 for acertain distance and forms a second gap 111. The acoustic through hole108 penetrates the first gap 110 and the second gap 111 to form an innercavity 112. When the MEMS microphone is powered on to work, the firstvibrating diaphragm 104 and the back plate 105, the second vibratingdiaphragm 106 and the back plate 105 will carry charges of oppositepolarity to form capacitance, when the first vibrating diaphragm 104 andthe second vibrating diaphragm 106 vibrate under the action of acousticwave, the distance between the back plate 105 and the first vibratingdiaphragm 104, between it and the second vibrating diaphragm 106 willchange, so as to cause changes in capacitance of the capacitance system,which in turn converts the acoustic wave signal into an electricalsignal to realize corresponding functions of the microphone.

In this embodiment, the first vibrating diaphragm 104 and the secondvibrating diaphragm 106 are square, round or elliptical. At least onesupporting part 109 is placed between the bottom surface of the firstvibrating diaphragm 104 and the top surface of the second vibratingdiaphragm 106.

The supporting part 109 is placed to penetrate through the acousticthrough hole 108 of the back plate 105 to fixedly connect the firstvibrating diaphragm 104 and the second vibrating diaphragm 106; i.e.,the supporting part 109 has no contact with the back plate 105 and noinfluence from the back plate 105.

The supporting part 109 can be formed on the top surface of the firstvibrating diaphragm 104 with all kinds of preparing technology, such asphysical vapor deposition, electrochemical deposition, chemical vapordeposition and molecular beam epitaxy.

The supporting part 109 can be constituted by semiconductor materialsuch as silicon or can comprise semiconductor material such as silicon.For example, germanium, SiGe, silicon carbide, gallium nitride, indium,indium gallium nitride, indium gallium arsenide, indium gallium zincoxide or other element and/or compound semiconductor (e.g., III-Vcompound semiconductor or II-VI compound semiconductor such as galliumarsenide or indium phosphide, or ternary compound semiconductor orquaternary compound semiconductor). It can also be constituted by orcomprise at least one of the followings: metal, dielectric material,piezoelectric material, piezo-resistive material and ferroelectricmaterial. It can also be made from dielectric material such as siliconnitride.

According to the embodiments, the supporting part 109 can be integrallymolded with the first vibrating diaphragm 104 and the second vibratingdiaphragm 106.

According to various embodiments, the second diaphragm 106 of thepresent invention includes a number of releasing holes 113. Thereleasing hole 113 is sealed with a dielectric material 114.

According to the embodiments, it also comprises the extractionelectrodes of the first vibrating diaphragm 104, the second vibratingdiaphragm 106 and the back plate 105, correspondingly a first electrode115, a second electrode 116, a third electrode 117.

According to various embodiments, the surface passivation protectionlayer 118 is also included.

Refer to FIG. 2, it also comprises a through hole 119 through the firstvibrating diaphragm 104, the supporting part 109, the second vibratingdiaphragm 106, the through hole 119, for example, is placed at thecentral position of the first vibrating diaphragm 104, the secondvibrating diaphragm 106, communicating the back cavity 102 with theexternal environment, thus resulting in a consistent external pressureof the first vibrating diaphragm 104 and the second vibrating diaphragm106.

Refer to FIGS. 3-4, it's a flow chart of an embodiment of amanufacturing method for a MEMS microphone provided by the invention,the manufacturing method is used to manufacture the microphone 100 asshown in FIG. 1 or FIG. 2, specifically it comprises the followingsteps.

Step S1, select a base, prepare the first vibrating diaphragm structureon the first surface of the base:

Specifically, it comprises the following sub-steps:

S11, a base 101 is selected and a first oxide layer 1071 is deposited onthe first surface 101A of the base 101, as shown in FIG. 4A.

The base 101, for example, is a semiconductor silicon substrate, or asubstrate of other semiconductor material such as: germanium, SiGe,silicon carbide, gallium nitride, indium, indium gallium nitride, indiumgallium arsenide, indium gallium zinc oxide or other element and/orcompound semiconductor (e.g., III-V compound conductor such as galliumarsenide or indium phosphide) germanium or and gallium nitride the like.

For example, the first oxide layer 1071 is silicon dioxide with athickness of about 1 μm, which is formed by conventional processes byadopting thermal oxidation and vapor deposition.

S12, the first polycrystalline silicon layer 1041 is deposited on thefirst oxide layer 1071, for example, the thickness of the firstpolycrystalline silicon layer 1041 is about 1 μm, as shown in FIG. 4B;

S13, etch the first polycrystalline silicon layer 1041. According to thestructural requirements of the first diaphragm 104, etch the firstpolycrystalline silicon layer 1041 to form the basic structure of thefirst diaphragm 104, as shown in FIG. 4C.

Step S2, prepare the back plate structure in the side space of the firstvibrating diaphragm structure opposite to the first surface of the base:

Specifically, it comprises the following sub-steps:

S21, the second oxidation layer 1072 is deposited on the first diaphragmstructure 104, the second oxidation layer 1072 such as 0.5 μm thickness,shown as FIG. 4D, preferably, in order to prevent the back plate 105from adhering with the first diaphragm 104, groove structure formed,prepared and bumped by the second oxidization layer 1072 can be etched.

S22, the back plate material layer is deposited. In this embodiment, theback plate structure includes a first silicon nitride layer 1051, asecond polycrystalline silicon layer 1052 and a second silicon nitridelayer 1053 stacked from the bottom to the top, wherein the first siliconnitride layer 1051 covers the second oxide layer 1071; the first siliconnitride layer 1051 and the second silicon nitride layer 1053 have athickness of about 0.25 μm, for example, and the second polycrystallinesilicon layer 1052 in the middle has a thickness of about 0.5 μm;

S23, etch the back plate material layer to form an acoustic through-hole108 arranged at intervals, as shown in FIG. 4F;

Preferably, the step of preparing bump on the surface of the secondsilicon nitride layer 1053 of the back plate is also included.

Step S3, prepare a second vibrating diaphragm structure in the sidespace of the back plate structure opposite to the first vibratingdiaphragm structure;

Specifically, it comprises the following sub-steps:

S31, a third oxide layer 1073 is deposited on the upper surface of theback plate and flattened, as shown in FIG. 4G; the flattening referredto in this embodiment adopts chemical mechanical polishing (CMP) processfor example.

S32, the third oxide layer 1073 is etched to form a deposition hole 1091of the supporting component 109, the deposition hole 1091 is located inthe acoustic through hole 108 of the back plate, exposing the uppersurface of the first diaphragm structure 104, as shown in FIG. 4H;

S33, a third silicon nitride layer 1092 is deposited to fill thedeposition hole 1091, as shown in FIG. 4I; the thickness of the thirdsilicon nitride layer 1092, for example, satisfies the requirement ofcompletely filling the deposition hole 1091, about 4 microns;

S34, remove the third silicon nitride layer 1092 other than the supportdeposition hole 1091, such as CMP process, as shown in FIG. 4J;

S35, the thickness of depositing the third polycrystalline silicon film1061 and the third polycrystalline silicon film 1061 for example is 1μm, shown as FIG. 4K;

S36, etching the third polycrystalline silicon film 1061 layer, forminga releasing hole 113; obviously, the releasing hole is located outsidethe supporting component 109, which is used to remove the oxide layerbetween the first polycrystalline silicon layer 1041 and the thirdpolycrystalline silicon layer 1061, which is located in the central mainarea, as shown in FIG. 4L.

S37, release the oxide layer, such as using BOE solution or HF gas phaseetching technology, remove the oxide layer under the thirdpolycrystalline silicon until the first polycrystalline layer isexposed; form the first isolation gap between the first polycrystallinelayer and the back plate and the second isolation gap between the thirdpolycrystalline layer and the back plate. Because the size of acousticthrough hole 108 on the back plate is larger than the size of supportingcomponent 109, the A connected cavity 112 is formed between the firstpolycrystalline layer 1041 and the third polycrystalline layer 1061, asshown in FIG. 4M.

S38 is used to seal the releasing hole. For example, a polymer, an HDPoxide layer or a phosphosilicate glass (PSG) reflux process is used toform a sealing layer, and the sealing layer is etched to remove theredundant sealing layer 114 outside the release hole area, as shown inFIG. 4N.

S39, etching the third polycrystalline layer 1061 to form the seconddiaphragm structure 106, mainly exposing the contact hole areas 1151,1161 and the edge area 120 of the MEMS microphone base 101, as shown inFIG. 4O;

Step S4, prepare a contact electrode.

Specifically, it comprises the following sub-steps:

S41, etch the contact hole. In the first step, etch the first contacthole 1151 in the back plate area, as shown in FIG. 4P, and etch the samedepth in the edge area 119; in the second step, etch the second contacthole 1161 in the first diaphragm 104 and the substrate silicon layer inthe edge area of the MEMS microphone, as shown in FIG. 4Q;

S42, a passivation protective layer 1181 is deposited on the surface ofthe whole device, the passivation layer is silicon nitride for example,as shown in FIG. 4R;

S43, etch the passivation layer to expose the contact areas 1152, 1171and 1162 of the first polycrystalline layer, the second polycrystallinelayer and the third polycrystalline layer. In addition, if TBD is oxide,the passivation layer on the TBD layer needs to be reserved, as shown inFIG. 4S;

S44, a metal layer is deposited and patterned, such as Cr and Cu alloy.The patterned metal layer makes the first polysilicon layer, the secondpolysilicon layer and the third polysilicon form conductive contactpoints on the upper surface of the device, that is, the lead outelectrode 115 led corresponding to the first diaphragm 104, the lead outelectrode 116 led corresponding to the second diaphragm structure 106,and the lead out electrode 117 corresponding to the back plate structure105;

Step 5, form the back cavity

Specifically, it comprises the following steps:

S51, the back surface of the base is thinned, for example, the backsurface of the base 101 is thinned by the grinding process;

S52, the second surface 101B of the patterned base is etched to form aback cavity area 102, and the etching stops at the first oxide layer1071, as shown in FIG. 4U;

S53, remove the first oxide layer 1071 in the back cavity area, andcomplete the MEMS microphone manufacturing, as shown in FIG. 4V.

Preferably, it also comprises the step of forming a through hole 119 ofthe supporting part through the central area of the device, to form theMEMS microphone as shown in FIG. 2.

In the manufacturing method of the MEMS microphone provided by theinvention, the preparation of the double diaphragm MEMS microphone iscompleted by using the standard semiconductor process, and is easy tointegrate with other semiconductor devices.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present exemplary embodiments havebeen set forth in the foregoing description, together with details ofthe structures and functions of the embodiments, the disclosure isillustrative only, and changes may be made in detail, especially inmatters of shape, size, and arrangement of parts within the principlesof the invention to the full extent indicated by the broad generalmeaning of the terms where the appended claims are expressed.

What is claimed is:
 1. A method for manufacturing a MEMS microphone including steps of: select a base, deposit a first oxidation layer on the first layer of the base; depositing a first polycrystalline silicon layer on a surface of the first oxide layer and graphing the first polycrystalline silicon layer for forming a first diaphragm structure; depositing a second oxide layer on the surface of the first diaphragm structure; depositing a material layer of back plate on the surface of the second oxidation layer; wherein the back plate material layer is patterned, and a plurality of acoustic through holes are formed in a middle main body area of the back plate material layer; depositing a third oxidation layer on the back plate structure, and flatten the third oxidation layer; wherein the third oxide layer and the second oxide layer are patterned to form a supporting component deposition hole between the acoustic through holes, and the deposition hole of the supporting component exposes the first diaphragm structure; depositing a material layer of supporting component to fill the deposition hole of supporting component; flattening the surface of the third oxide layer to remove the supporting component material layer of supporting component outside the deposition hole of supporting component; depositing a third polycrystalline silicon layer on the flattened surface of the third oxide layer to form a second diaphragm structure; graphing the third polycrystalline silicon layer to form a plurality of releasing holes; wherein the second and third oxide layers between the first polycrystalline silicon layer and the third polycrystalline silicon layer and within the range of the middle main body area of the back plate are removed through the releasing hole to form an inner cavity; depositing a sealing material layer on the third polycrystalline silicon layer for sealing the releasing hole, wherein the sealing material layer is patterned to remove the redundant part; preparing an extraction electrodes of the first vibrating diaphragm structure, the second vibrating diaphragm structure and the back plate structure; back-etching the base to form a back cavity area corresponding to the central main body area of the back plate structure.
 2. The method for manufacturing the MEMS microphone as described in claim 1, wherein the step of depositing of the material layer of back plate comprises step of depositing a first nitride silicon layer, a second polycrystalline silicon layer and a second nitride silicon layer.
 3. The method for manufacturing the MEMS microphone as described in claim 2, wherein the step of depositing of the extraction electrodes of the first vibrating diaphragm structure, the second vibrating diaphragm structure and the back plate structure comprises steps of: etching for forming electrode extraction holes of the first vibrating diaphragm structure, the back plate structure and the second vibrating diaphragm structure; depositing and visualizing the electrode layer, form the first extraction electrode of the first vibrating diaphragm structure, the second extraction electrode of the second vibrating diaphragm structure, the third extraction electrode of the back plate structure.
 4. The method for manufacturing the MEMS microphone as described in claim 1, wherein the step of forming back cavity comprises steps of: thinning and etching the base from the second surface of the base; eliminating the first oxidation layer under the first vibrating diaphragm structure and corresponding to the back cavity structure.
 5. The method for manufacturing the MEMS microphone as described in claim 1, wherein a step of depositing a passivation protective layer after forming an electrode outlet hole is further included.
 6. The method for manufacturing the MEMS microphone as described in claim 1 including at least one through hole through the first diaphragm structure, the supporting component and the second diaphragm structure for communicating the back cavity with the external environment.
 7. The method for manufacturing the MEMS microphone as described in claim 1, further comprising a step of forming a bump on the upper and lower surfaces of the central main body area of the back plate structure.
 8. The method for manufacturing the MEMS microphone as described in claim 1, wherein the material of the supporting component includes silicon nitride.
 9. The method for manufacturing the MEMS microphone as described in claim 1, wherein the electrode material includes Cr and Au. 